This invention relates to a musical tone producing device of a waveshape memory readout type and, more particularly, to a control for realizing a tone color change of a waveshape in accordance with a tone color change parameter such as a key touch or tone pitch read out from a waveshape memory.
It has recently been practiced in the art to store a full waveshape from the start to the end of sounding of the tone or a rise portion and a part of subsequent waveshape portion and, in the case of storing the former, produce a tone of a good quality by once reading out the full waveshape and, in the case of storing the latter, produce a tone of a good quality by reading out a waveshape of a rise portion once and then the part of subsequent waveshape repeatedly.
U.S. Pat. No. 4,383,462 discloses an electronic musical instrument which aims at producing a tone of a high quality by prestoring a full waveshape from rising to termination of sounding of the tone in a memory and reading out the waveshape therefrom. In the waveshape memory WM31 in FIG. 3 of this United States patent, a full waveshape is stored and this full waveshape is read out in response to a signal KD which represents a key depression timing. Such system in which the full waveshape is stored requires a large memory capacity.
In order to improve this point, it has been conceived to store a part of waveshape of plural periods out of the complete sounding period in a waveshape memory and obtain a tone signal by repeatedly reading out the partial waveshape. In the above U.S. Pat. No. 4,383,462, an example of such improvement is shown in FIG. 6. A complete waveshape in the attack period is stored in the waveshape memory WM61 and at least one fundamental period of a tone waveshape is stored in the waveshape memory WM62. An attack waveshape is read out from the memory WM61 in response to the key depression (KD signal) and the tone waveshape of the fundamental period is repeatedly read out from the memory WM62 after completion of the readout of the attack waveshape (IMF signal) until the end of tone generation (DF signal).
If such waveshape memory system is applied without any modification for realizing various tone color change corresponding to tone color change parameters such as the key touch or tone pitch, many different waveshapes in a memory must be prepared in correspondence to all kinds of key touches or tone pitches used. This requires a tremendous memory capacity and therefore is unrealistic.
It is then conceivable to prepare two kinds of continuous waveshapes such, for example, as a continuous waveshape corresponding to the strongest touch and a continuous waveshape corresponding to the weakest touch when key touch strength is used as a tone color change parameter, in a waveshape memory and read out the two waveshapes simultaneously and interpolate them in accordance with the tone color change parameter (i.e., touch strength) thereby producing a new waveshape corresponding to the tone color change parameter (touch strength). In actuality, however, the interpolation would be meaningless unless the two waveshapes to be interpolated were in phase with each other. Since duplicates of waveshapes of tones produced by an actual performance are used as the two types of waveshapes to be prepared in the waveshape memory, the phases of the two waveshapes are very different in general so that the two waveshapes which have been brought in phase with each other at the start point thereof will be greatly out of phase several seconds later. This system, therefore, is also unrealistic.
It is, therefore, an object of the present invention to realize various tone color changes by a relatively small-scale and low cost construction in a musical tone producing device of full waveshape readout type with improved tone quality.